Ultrasonic burner



1965 J. c. O'CONNOR YOUNG ETAL 3,200,873

ULTRASON I C BURNER z Sheets-Sheet 1 Filed June 4, 1962 H mmDgu John C.O'Connor Young Robert J. Long PATENT ATTORNEY 1965 J. c. O'CONNOR YOUNGETAL 3,200,873

ULTRASONIC BURNER Filed June 4, 1962 2 Sheets-Sheet 2 FIGURE II FIGURE11'.

John C. O'Connor Young Robert J. Long INVENTORS domes A. Wilson BY 7M0.

PATENT ATTORNEY United States Patent 3,2-tlt9,873 llllbT-itAlOhlllfiP-URNER John Q. GiConncr Young, Staten Island, N.Y., and Robert ll.Lang, 'Watchung, and Issues A. Wilson, Stanhope, Nah, assignors to EssoResearch and Engineering Com= parry, a corporation of Delaware Filed.iune 4, 1962, Ser. No. 199,738 12 Qiaims. (Ql. 158-77) The presentinvention relates to a liquid fuel burner. It relates more specificallyto a burner which utilizes an ultrasonic atomizer. Units made accordingto this invention may be of various sizes and capacities, but theinvention has particular applicability to fuel burners operating at lowconsumption rates.

In the prior art, numerous liquid fuel burners, particu larly thoseoperating on petroleum distillates, have been used successfully all overthe world. Conventional burners which use high pressure nozzles arereliable at high oil rates. However, at rates below 0.6 gallon per hourthe conventional burners are not reliable. The tiny swirl slots neededto obtain fine atomization at low rates are prone to plugging.

There is a need for a reliable burner capable of operating at low firingrates. For example, such a burner is ceded for domestic hot waterheaters and for homes in relatively mild climate.

It is, therefore, an object of this invention to provide a burner whichis reliable at oil rates below 0.6 gallon per hour.

Other objects will be apparent as one reads the description of theinvention.

The objects of this invention are achieved by utilizing a specific andparticularly eificient ultrasonic atomizer in a burner systemspecifically designed to enhance the reliability of the atomizer.

The invention is best understood by referring to the accompanyingdrawings wherein:

FIGURE I is an elevational view, partly in section, depicting apreferred type of unit.

FIGURE II is a cross-sectional view taken at section 2-2 of FIGURE I.

FIGURE III is a cross-sectional view taken at section 3-3 of FIGURE I.

Referring first to FIGURE I, a controller 2 is shown. The circuitry ofthe controller is not shown herein as the controller is of theconventional type. For example, General Electric CR7865A101A mastercontroller can be used in this system. A suitable motor 1 connected tothe controller 2 by leads '7 and 9 drives oil pump 11 and blower 13. Theoil pump 11 transfers fuel oil from a suitable source, not shown,through line 15 to the ultrasonic atomizer to be described below. Unlikea gun burner, the ultrasonic burner does not require a high pressure oilsuppl Therefore, a simple low torque pump, such as a gear pump, may beused in conjunction with a cheap shaded pole motor. If the low torquepump is used, it is necessary to employ a solenoid controlled blockingvalve 17. Alternatively, a high torque pump can be used. In thealternative system, it is necessary to employ a clutch, e.g.,centrifugal clutch, to engage the motor and the pump. A high torque pumpacts as a blocking valve when not operating, thus valve 17 may beexcluded, if the alternate system is used.

The blower or 13 can be of the squirrel cage or cylinder type, as shown,or any other suitable type. The blower supplies ambient air to thesystem. The air is blown through the space between the atomizer assemblyand the more or less conventional blast tube 19, and is admixed with theatomized oil. Secondarily, but importantly, the air serves to cool thetransducer, thereby prolonging the life of the burner.

masts "ice The atomizer assembly is an integral unit comprising theultrasonic atomizer, two ignition electrodes, a heat shield, and a flamesensing device.

The ultrasonic atomizer is essentially the device described in copendingapplication Serial Number 122,308, filed July 6, 1961. A briefdescription will sufiice for the purposes of this invention. Theatomizer comprises two stepped horn units 21 and 23. These are placed ina base-to-base relationship with a piezoelectric crystal disc 24 betweenthem. The disc is made of a piezoelectric ceramic, such aslead-zirconium titanate.

The stepped horns 21 and 23 are held in compression against thepiezoelectric disc 24, by mechanical clamping means comprising front andrear flanges 25' and 26 and studs connecting such flanges. The studs 27and 23 are shown in FIGURES II and III. The studs enter the rear flange26 and are screwed into the front flange 25.

As is seen in FIGURE I, the front fiange contacts th first stepped horn21 at the periphery of the shoulder of the stepped horn in order tominimize damping of the ultrasonic atomizer. As is explained incopending application Serial Number 122,308, the atomizer is designed sothat planes of essentially zero displacement exist at the shoulders ofthe stepped horns. The rear flange contacts the second stepped horn 2.3at the periphery of the shoulder of said horn. In the particular designshown, it is necessary that a suitable insulating material, for example,mylar, be placed between the rear flange and the second stepped horn.

An axial hole 27 is drilled in the tip of the first stepped horn 21. Theaxial hole extends back to a radial hole located essentially at avibrational node in the horn. The radial hole is located near a nodalpoint so that the oil feed line 15 can be attached to the side of theborn without damping the atomizer.

The stepped horns are made of a suitable material, for example,aluminum. For the purposes of this invention the first stepped horn ismodified in at least three respects. The tip of the stepped horn ispreferably filleted at 34 in order to reinforce the tip so that it canwithstand a high degree of stress. A groove 3G is formed around the tipof the first stepped born. This prevents oil from creeping back alongthe horn. If the oil were not prevented from creeping back alom thehorn, it would accumulate in the space 31 between the shoulder of thehorn and the front flange 25. This could damp the atomizer and thusrender it less effective or even inoperable.

Another modification of the first stepped horn is also desirable. Thedisc of piezoelectric material 24 must be kept at relatively lowtemperatures in order to ensure the reliability of the system. If thedisc is subjected to relatively high temperatures, for example,temperatures above 1 for prolonged periods, it will be depolarized. Asmentioned before, the atomizer is cooled by the combustion air suppliedby the blower 13. However, at low oil rates, the how rate of air isgreatly diminished.

In order to protect the piezoelectric material from heat, a portion ofthe aluminum stepped horn 2:1 is replaced by a disc of stainless steel32. Stainless steel has a thermal conductivity of about one-tenth thatof aluminum. Moreover, it has sonic properties approaching those ofaluminum.

To further protect the atomizer, a heat shield 33 is attached to thefront flange in order to reduce the amount of radiant heat input to theatomizer.

Ignition of the fuel-air admixture is accomplished by an arc formedbetween two electrodes. The positions of the electrodes 35 and 37 arebest observed in FIGURES II and III. The electrodes are fastened to therear flange 26 by means of a fiber clamp As shown in FIGURE 1, electrode35 is inserted through the heat shield 33 and is 3 fitted into anelectrode guide 39 which is drive fitted into the front flange 25.Electrode 37, not shown in FIGURE I, is mounted in like manner. Theelectrodes are insulated with .a suitable material, for example,porcelain. Ignition is accomplished by an are formed across theelectrode tips 40 and 41, shown in FIGURE III.

The atomizer assembly is also equipped with a flame detector 43 which ismounted through the rear flange and extends through the front flange andheat shield. A flame detector, such as the one described in copendingapplication Serial Number 128,846, now abandoned, can be used in thissystem. The flame detector upon seeing the flame sends a signal to .thecontroller which breaks the circuit to the ignition transformer 45. Ifno flame is established, the controller 2 will shut down the burner,repeat the cycle and then lock the system out.

The atomizer unit is fitted into a turbulator tube 46 which has vanes47, d8, 39, 50, 51 and 52, shown in FIGURE III, around its periphery.These vanes are tacked to the blast tube 19. Attached to the end of thblast tube is an end cone 53 which serves to channel the combustion airto ensure efiicient combustion. The atomizer unit need not be attachedto the turbulator tube. In fact, it is preferred that it merely fitsnugly in said tube. This allows the convenient removal of the atomizerunit for maintenance. The vanes of the turbulator tube serve to impart acentrifugal force to the combustion air. In the prior art devices vaneshave been employed. However, t-here is usually a large central spacethrough which the air can .pass. Thus, only a small portion of the aircomes under the influence of the vanes. For the purposes of thisinvention, it is highly desirable that the front flange 25 blocks offthe air flow so that all the combustion air is forced to flow in theannular space between the turbulator tube and the blast tube. Thus, allthe combustion air comes under the influence of the vanes and a greatercentrifugal force is imparted thereto. This results in a greatercombustion eificiency and it also results in moving the flame away fromthe burner tip. These functions are especially important at low oilrates and correspondingly low combustion air flow rates.

Moving the flame away from the burner tip protects the tip from thedestructive combustion. Moreover, it reduces the amount of heattransferred to the atomizer, thus lowering the temperature in the areaof the piezoelectric material. Thus, it is seen that using a designherein suggested results in increased combustion efficiency, protectsthe tip of the atomizing transducer and prolongs the life of thepiezoelectric material.

The atomizer is supplied wit-h power by an electronic driver oroscillator 55 which is connected with electric mains 57 and 58 by leads59 and 60. The driver is connected to the atomizer with leads 62. and63. The input lead 62 is connected with a post 64 which is imbedded inthe fiber clamp 38. It is necessary that the post 64 does not extendthrough the fiber clamp and make contact with the rear flange 2d. Thepost 64 is connected with the second stepped horn 23 by lead 66. Asshown in FIGURE II, return lead 63 is connected with post 65 whichextends through the fiber clamp and is screwed into the rear flange.

The driver 55 is essentially the one described in copending applicationSerial Number 59,335, filed September 29, 1960 now Patent No. 3,121,534issued February 18, 1964-. The driver supplies power at a frequencywhich corresponds with the natural resonance of the atomizer or one ofthe major harmonics thereof. The frequency will depend upon theparticular design of the sonic atomizer, but will usually be within therange of from 20,000 to 230,000 cycles per second. It is preferred thatthe atomizer be designed to have a resonant frequency within the rangeof from 50,000 to 100,000 cycles per second.

The sonic atomizer converts the electrical energy into mechanical energydue to the cyclic expansion and contraction of the piezoelectricmaterial. As described in copending application Serial Number 122,308,the transducer is designed so that a displacement antinode exists at thetip of the stepped horn. Thus, the vibrations of the horn atomizes theoil emerging from the horn into particles having a mass median particlediameter of 125 microns or less.

The ignition electrodes 35 and 37 are connected to the ignitiontransformer with leads 6'7 and 69. Lead 59 is connected with electrode35, as shown in FIGURE I, and lead 67 is connected with electrode 3'7,as shown in FIGURE II.

The ignition transformer steps up the line voltage of 115 volts to avoltage, e.g., 15,000 volts, suificient to cause an arc across electrodetips 40 and 41.

In order to integrate the driver 55 into the rest of the control circuitand to ensure that oil cannot be injected into the atomizer before thedriver and transducer are operating suitably, a simple but unique delaymeans is employed. A coil 72 is inductively coupled with the plateinductance 74 of the driver. The coil is connected to the heaterresistance of a thermal delay switch 53, and the switch is connectedacross the thermostat terminals of the conventional controller 2.

In operating this burner, thermostat 54- upon receiving the desiredstimulus completes the circuit which is supplied with 115 voltalternating currentby electric mains 57 and 58. The electronic driver 55transmits power to the atomizer via leads 62 and 63 at the resonantfrequency of the atomizer.

As the driver warms up, current is transmitted to the normally openthermal delay switch 73. The switch closes completing the circuitsupplied with 115 volt alternating current by electric mains 70 and 71to activate the controller.

The controller supplies the ignition transformer with voltage via leads5'7 and 69. The transformer steps up the voltage to an amount sufiicientto cause an arc to form across the electrode tips 40 and 51. Current issupplied to the solenoid via leads 78 and 79. The solenoid then opensvalve 1'7 to permit the passage of oil. The motor 1 is connected to thecontroller by leads 7 and 9. The motor drives the oil pump 11 and oil ispumped through feed line 15 at a rate of from 0.2 to 1.0 gallon per hourand higher.

The motor also drives the fan or blower 13 which supplies air at a rateof from 6 to 30 cubic feet per minute and higher, depending upon the oilrate. The flow of air is adjusted by a manual control valve, not shown.The oil passes into the radial hole 28, through the axial hole 27, isatomized by the vibration of the stepped horn, and emerges from the tipof the first stepped horn 21 to be admixed with the combustion air whichhas flowed past the atomizer and between the turbulator tube 46 and theblast tube 19. The air-oil admixture is ignited by the are formed acrossthe electrode tips 40 and 41.

The flame sensing device or photocell 43 sees the flame and sends asignal to the controller 2 which breaks the circuit to the transformerand turns ofi the arc.

The burner described herein was fired with #2 heating oil at ratesbetween 0.2 and 0.7 gallon per hour. Clean combustion at high stack gasCO levels above 10% was obtained throughout this range.

The durability of the ultrasonic burner was tested under a variety ofconditions. A life test of 0.5 gallon per hour and a C0 level of 10% wasvoluntarily concluded after a successful 5,000 hours of firing.

At the time of filing, a burner fired at a rate of 0.25

gallon per hour had been successfully operating for 1,000 hours.

The invention has been described with a certain degree of particularity.It will be obvious that other modifications may be made consistent withthe invention by those skilled in the art. It is intended by thefollowing claims to cover such modifications and variations as areproperly a part of this invention so far as permitted by the prior art.

What is claimed is:

1. In a burner for liquid fuels, the combination which comprises:

an ultrasonic fuel atomizer comprising a vibratory horn element having asubstantially non-vibratory nodal point, an inlet for fuel adjacent saidnodal point;

a pump for supplying fuel to said atomizer and a blower for supplyingcombustion air in admixture with atomized fuel emerging from saidatomizer;

electronic drive means for said atomizer;

valve means for controlling the flow of fuel from said pump to theatomizer, and control means associated with said electronic drive meansfor preventing the flow of fuel from the pump to the atomizer when poweris not being supplied to said drive means.

2. A burner according to claim 1 wherein a heat shield is placed betweenthe burning atomized fuel and the ultrasonic fuel atomizer.

3. A burner in accordance with claim ll wherein said ultrasonic atomizercomprises a stepped-horn resonator with an atomizing tip of reduceddiameter, a disc of piezoelectric material and means formed in saidatomizing tip for preventing liquid fuel from creeping back along theexternal surface of said tip.

4. A burner according to claim 3 wherein a metal disc is placed betweensaid resonator and said disc of piezoelectric material; said metal dischaving sonic properties approaching those of the resonator and a thermalconductivity substantially less than that of the resonator.

5. A burner according to claim 3 wherein said steppedhorn resonator ismade of aluminum and a disc of stainless steel is placed between saidresonator and said disc of piezoelectric material.

a. A burner unit capable of operating at liquid rates 610W 0.6 gallonper hour comprising in combination:

an ultrasonic fuel atomizer having a fuel atomizing end part, saidatomizer also having a substantially non-vibratory nodal point remotefrom said part;

means for supplying liquid fuel to said atomizer adjacent said nodalpoint;

a blower for supplying combustion air to the burner unit, includingmeans for channeling such combustion air so that said air is admixedwith the atomized fuel; electronic drive means for said atomizer;

turbulating means surrounding the atomizer and annularly spacedtherefrom for swirling the combustion air prior to its admixture withthe atomized fuel and means for directing the flow of said air so thatessentially all of the combustion air comes under the influence of saidturbulating means; and

igniting means for initiating combustion of the fuelair admixture.

7. A burner unit according to claim 6 wherein combustion detector meansresponsive to visible flame are provided to prevent operation of saidigniting means when visible flame persists.

8. A combination according to claim 6 which includes:

a conventional controller for coordinating igniting means, blower, andmeans for supplying liquid fuel; and

control means for integrating said electronic drive means with saidcontroller so that said. controller is not activated until power issupplied to said drive means.

9. A burner unit according to claim 8 wherein said control meanscomprises a delay switch connecting said electronic drive means withsaid controller.

1d. For use in a liquid fuel burner, a high frequency transduceratomizer comprising a stepped horn resonator with an atomizing vibratingtip of reduced diameter and having a relatively non-vibrating nodalpoint behind said tip, means for introducing fuel into said resonatornear said nodal point, means comprising a disc of piezoelectric materialattached to said resonator for transmitting vibratory energy thereto,means for forcing liquid fuel from nodal point to said tip, and meansformed in said resonator for preventing liquid fuel from creeping backalong the external surface of said tip towards said nodal point.

11. A transducer atomizer according to claim 111 wherein a metal disc isplaced between said resonator and said disc of piezoelectric material;said metal disc having sonic properties approaching those of theresonator and a thermal conductivity substantially less than theresonator.

32. A transducer atomizer according to claim 11 wherein said steppedhorn resonator is made of aluminum and said disc is composed ofstainless steel.

References Eited by the Examiner UNl'lED STATES PATENTS JAMES W.WESTHAVER, Primary Examiner.

PERCY L. PATRICK, MEYER PERLIN, Examiners.

1. IN A BURNER FOR LIQUID FUELS, THE COMBINATION WHICH COMPRISES: ANUTRASONIC FUEL ATOMIZER COMPRISING A VIBRATORY HORN ELEMENT HAVING ASUBSTANTIUALLY NON-VIBRATORY NODAL POINT, AN INLET FOR FUEL ADJACENTAAID NODAL POINT; A PUMP FOR SUPPLYING FUEL TO SAID ATOMIZER AND ABLOWER FOR SUPPLYING COMBUSTION AIR IN ADMIXTURE WITH ATOMIZER FUELEMERGING FROM SAID ATOMIZER; ELECTRONIC DRIVE MEANS FOR SAID ATOMIZER;VALVE MEANS FOR CONTROLLING THE FLOW OF FUEL FROM SAID PUMP TO THEATOMIZER, AND CONTROL MEANS ASSOCIATED WITH SAID ELECTRONIC DRIVE MEANSFOR PREVENTING THE FLOW OF FUEL FROM THE PUMP TO THE ATOMIZER WHEN POWERIS NOT BEING SUPPLIED TO SAID DRIVE MEANS.